<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>login 表单</title>
</head>
<body>
<form method="post">
  <div>
    <label for="user">用户名</label>
    <input name="username" id="user" placeholder="输入用户名">
  </div>
  <input type="submit" value="提交按钮">
  <div>
    <p>{% if  error %} {{ error }} {% endif %}</p>
  </div>
</form>

</body>
</html>